1. Field of the Invention
The present invention relates to a chain formed by a plurality of inner links and outer links coupled together alternately and pivotally in the longitudinal direction and placed over a sprocket. The chain is used as a transmission chain, for example.
2. Description of the Related Art
Chains that are placed over a sprocket are generally formed by a plurality of inner links and outer links. The inner link has a pair of inner link plates and a pair of bushings press-fitted in the link plates. The outer link has a pair of outer link plates and a pair of connecting pins press-fitted in the link plates. The connecting pins of each outer link are loosely fitted in the bushings of each inner link so that the inner links and the outer links are alternately and pivotally coupled together in the longitudinal direction of the chain (hereinafter referred to as “longitudinal direction”).
One known chain uses inner links that are formed as a single piece component to include a pair of inner link plates and a pair of bushings by a single piece forming process (for example, second to fourth columns and drawings of Japanese Examined Utility Model Application Publication No. H2-10848).
The pair of bushings of the inner links of the conventional chain cause the tensile force to be applied as pressing force to a pair of non-facing portions of the inner link plates that are opposite from the pair of facing portions where the link plates face each other in the longitudinal direction.
In the inner link plates, therefore, tensile stress is concentrated (hereinafter, “concentrated tensile stress”) in portions surrounding the respective bushings, at boundary portions around the boundaries between the facing region, which is an area between a pair of facing portions facing each other in the longitudinal direction, and the non-facing region, which is an area between the pair of non-facing portions in the longitudinal direction.
Such concentrated tensile stress repeatedly generated as a result of fluctuation of tensile force decreases the fatigue strength of the inner link plates and lowers the durability of the chain.
The applicants of the present invention have proposed a chain formed by coupling together link units and pairs of link plates alternately in the longitudinal direction, the link units each having a pair of connecting pin portions and a pair of plate portions integrally joined together at joint parts, and the pairs of link plates each being coupled to the connecting pin portions such as to be pivotable around a pivot center line.
In the proposed chain, the pair of connecting pin portions apply the tensile force as pulling force to the respective plate portions via the joint parts located in facing portions facing each other in the longitudinal direction, so that the concentration of tensile stress in conventional chains is prevented, and the chain can have improved durability as a result of increased fatigue strength of the plate portions.
One problem in the proposed chain is that, as the link units and link plates can pivot around the pivot center line relative to each other, if plate portions and link plates adjacent each other in the width direction of the chain contact each other in a large area, the friction resistance is accordingly large as the link units and link plates slide on each other when the chain bends, so that power loss in the chain is increased.